Allied Telesis AT-iMG634 - R2 User's Guide download pdf (Page 187)

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Overview BRIDGE

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iMG/RG Software Reference Manual (Switching)

2.3 BRIDGE

2.3.1 Overview

The Bridge module acts as an extension to the existing Layer 2 switch - providing connectivity between the

applications and services provided in the CPU and the devices connected to the LAN ports also provides sup-

port for virtual LANs in order to create multiple domains in which the packets are forwarded. The Bridge mod-

ule also provides standard interfaces for attachment to the system TCP/IP Stack allowing the termination of IP

frames belonging to a specific VLAN to a well defined IP interface.

A key point of interest here is that the port associated with the Bridge is not the Ethernet Port from the switch

- there is a single interface between the switch and the bridge, and then additional connections to the different

functions - such as the ADSL interface - or the IP interface.

2.3.2 Bridge Functional Description

2.3.2.1 Source MAC based forwarding

The source based MAC forwarding entries are unicast entries configured to forward packets on the specified

port that is configured for the MAC address, which matches the destination MAC address of the packet. They

are also used to restrict forwarding of packets to the ports specified in the entry if MAC address and source

port matches the source MAC address of the packet and the port on which packet is received.

The source based MAC entries (named also static unicast entries source based) can be created/deleted by the

user through. These entries have higher priority over the dynamic entries, meaning that the learned entry does

not overwrite the static unicast entry with the same MAC address.

A static unicast entry serves the following purpose in packet forwarding:

• For a packet received from the port with its source MAC address and received port matching the static uni-

cast entry’s MAC address and the source port respectively, then the packet will be forwarded to the respec-

tive ports as specified by the entry’s destination mask;

• For a packet received from a port with its source MAC address matching but withdifferent source port, the

packet will be discarded;

• For a packet received from a port with its destination MAC address matching a static unicast entry, the

packet will be forwarded to the source port of the entry.

2.3.2.2 Destination MAC based forwarding

The destination based MAC forwarding entries are configured to forward packets to the ports specified in the

entry whose MAC address matches the destination MAC address of the packet. In the absence of a static uni-

cast entry or a dynamic entry, it provides the capability to forward unicast packets to the ports on which the

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